The objective of this project is to characterize some of the fundamental mechanical, biochemical, and histochemical properties of non-neurogenic skeletal muscle atrophy in cats and rats. Three means of inducing muscular atrophy will be used: 1) immobilization produced by skeletal fixation, 2) parenteral administration of a catabolic steroid, and 3) a combination of immobilization and steroid treatment. A secodary objective is to assess the abiliy of various exercise programs to palliate muscular atrophy produced by steroid administration. Unilateral immobilization will be produced by internal fixation of the knee and ankle joints using surgical pins. Chronic electromyographic recordings frm the immobilized and contralateral control legs will be used to determine the extentof relative and absolute muscular actiities in the calf musculature. Daily subcutaneous injections of triamcinolone will be used to produce muscular atrophy without restricting normal muscular movement. Daily treadmill running will be used to stress the endurance capacity of steroid-treated animals, while daily vertical climbing with attached weights will present steroid-treated animals with a repetitive, high resistance stress. The combination of immobilization and steroid administration will help define the "pure" atrophic effects of steroids by eliminating isotonic movement. After four weeks of treatment, the degree of muscular atrophy, histochemical staining patterns, contractile properties, glycolytic and oxidative profiles, and fractional protein concentrations will be determined in gastrocnemius and soleus muscles.. BIBLIOGRAPHIC REFERENCES: Crockett, J.L., and Edgerton, V.R. Exercise and restricted activity effects on reinnervated and cross-innervated skeletal muscles. J. Neurol. Sci. 25: l-9, l975. Gerchman, L., Edgerton, V.R., and Carrow, R. Effects of longterm physical activity on the histochemistry and morphology of the ventral motor neurons. Exp. Neurol. 49: 790-801, l976.